In the catalytic processing of petroleum feedstocks, it is often desirable to alter the pore structure of the catalyst in order to accommodate different types of feeds. For example, when processing feedstocks of high metals content, the metals tend to deposit rapidly on the catalyst surface and plug the pores of conventional hydroprocessing catalysts, resulting in a loss of catalytic activity for sulfur removal. To facilitate the diffusion of large components into and out of the catalyst and to prevent surface deposits of coke and metals, large pore diameters are required. On the other hand, when processing feedstocks with no metals or with low metals contents, it may be technically and economically desirable to use a narrow-pore catalyst. The catalysts prepared according to the present invention are narrow-pore catalysts which have high desulfurization and hydrogenation activities.
It is known that in certain hydrocracking operations the hydrocracked products are contaminated with mercaptans, even in cases where the initial feed placed in the hydrocracking zone is free of mercaptans. There is, therefore, a need to eliminate mercaptans from the hydrocracked products. In addition to being useful for a variety of hydrotreating applications in which high desulfurization and hydrogenation activities are required, the catalysts of the instant invention are particularly useful as a non-acidic post-treatment for hydrocracked products which are contaminated with mercaptans. These mercaptans are apparently synthesized during or after hydrocracking operations by the reaction of olefins with hydrogen sulfide, as exemplified by the equation: EQU CH.sub.2 .dbd.CH.sub.2 +H.sub.2 S.revreaction.CH.sub.3 CH.sub.2 SH
This reaction is catalyzed by the acidic nature of the hydrocracking catalysts used in the hydrocracking zone. It has been found that the catalysts prepared according to the invention, which have high hydrogenation and desulfurization abilities, prevent the reaction of olefins and hydrogen sulfide to mercaptans by hydrogenating the olefins, or, alternatively, reduce the concentration of the mercaptans which are formed by conventional desulfurization.